1. Field of the Invention
This invention relates to an aquatic antifouling composition for preventing ship-bottoms, fishnets such as nursery nets and stationary nets, and other marine structures from being fouled or injured by marine adhesive livings.
2. Description of the Prior Art
Ships, specifically their bottoms and waterline zones, fishnets such as nursery nets and stationary nets, and other marine structures are subject to adhesion and parasitism of various marine organisms: they include animals such as barnacles, hydroides, ascidians, hard-shelled mussels and oysters, algae such as sea lettuce, green laver and marine-spirogyra, and various bacteria, molds and diatoms called slime. Their adhesion affects the ships and so forth seriously. A great cost is required for removal of these organisms and repairment or repainting of the ships, etc.
In the case of a ship, for example, a several percent increase in the resistance of its hull due to the adhesion of such marine organisms causes a decrease in the speed and a fall in the fuel efficiency, which would result in a serious loss.
Recently the advance of ocean development in the coastal regions has been encouraging construction and installation of large marine structures, structures annexed thereto, and other similar structures. The structures exposed to sea water, for example, structures for harbor facilities such as nautical beacons, floating beacons, mooring buoys, floating piers, floating breakwaters , and floating docks, pipelines, bridges, tanks, water pipes in power stations, seaside industrial plants, mooring ships, mooring and floating fishing structures, fish preserving structures, and stationary nets and other structures for fishing facilities, suffer various damage such as corrosion in the basal parts, sinking due to the increased weight, loss of balance, etc. when the pollution-productive marine organisms have adhered and grown there.
At facilities, plants, and power stations located along seashores, when they use sea water for cooling or for the other purposes, the pollution-productive adhesive marine organisms adhere to their seawater inlets and outlets, coastal structures such as channels and culverts, and gain growth there. The volume occupied by these organisms at times reaches the order of some tens of percents of the inner volume of such tubular structures, which causes a decrease in the available cross-sectional area of waterways, an increase in the resistance to the liquid flow, choking of the screens to remove suspending solids, and so forth.
Fishnets such as nursery nets and stationary nets and marine ropes are subject to adhesion of such marine organisms as barnacles, hydroides, ascidians, green lavers and brown lavers. Since their adhesion impairs the economic use of such nets and ropes, great labor and large expense are required for the maintenance of such nets and ropes.
Heretofore, for the protection of marine structures from the adhesion of harmful marine organisms, sparingly soluble inorganic copper compounds, organic tin compounds, organic tin polymers, and organic nitrogen-sulfur compounds have been used.
These substances, however, have various drawbacks; some manifesting toxicity to men and beasts, others polluting environments, and yet others failing to maintain sufficient effect when used for a long time as an aquatic antifoulant. For example, organic tin compounds are highly effective in preventing the adhesion of marine organisms, and they have been regarded as efficient antifouling components and widely used. Recently, drawbacks of these organic tin compounds-being sparingly degradable, accumulation in living bodies, toxicological problem against men and beasts, possibility to cause environmental pollution-have been drawing attention.
Like organic tin compounds, dithiocarbamates which are organic sulfur compounds are also widely used as antifouling components. For example, Japanese Unexamined Patent Publication No. Sho 51-49227 discloses that adhesion of harmful marine organisms is prevented by coating fishnets with a composition obtained by combining manganese ethylenebisdithiocarbamate as an antifouling component with a vehicle. Also, Japanese Unexamined Patent Publication No. Sho 51-51517 discloses that adhesion of such harmful organisms is prevented by coating fishnets with an antifouling composition obtained by combining a heavy metal salt of ethylenebisdithiocarbamic acid, a cellulose resin and a vehicle.
As antifouling components against aquatic or marine organisms, organic tin compounds represented by tributyltin hydroxide, triphenyltin hydroxide and the like, tin-containing copolymers of such monomers as tributyltin (meth)acrylate, triphenyltin (meth)acrylate, bis(tributyltin)fumarate and the like, tin-containing copolymers comprising the said monomers and vinyl monomers are considered most desirable in terms of retention of efficacy and stability of effect. However, use of them are almost forbidden because of their dangerous property against men and beasts, their possibility to cause environmental pollution and so forth.
In terms of safety to men and beasts and freedom from environmental pollution, metal salts of dithiocarbamic acid are rated as the most desirable antifouling components for antifoulants. In many cases, however, they are not satisfactory in terms of retention of efficacy and stability of effect. In order to solve these problems, a heavy metal salt of alkylenebisthiocarbamic acid is combined with an inorganic copper compound to prepare an antifouling component, or some other antifouling components such as organic tin compounds are added to the said combination. This practice, however, does not achieve satisfactory results. In the circumstances, an aquatic antifouling composition which is able to retain its effect long, which is sparingly susceptible to physical or chemical deterioration when coated, which is highly safe to men and beasts, and at the same time which is little liable to cause environmental pollution has been desired.